This invention relates generally to apparatus that project electromagnetic radiation over a predetermined spherical sector and, more particularly, to apparatus that project electromagnetic radiation with a tailored intensity distribution.
Apparatus of this particular kind are commonly used to project electromagnetic radiation, especially visible light, over a hemisphere, i.e., 2 .pi.steradians, for a variety of applications. Examples of such applications include use as a warning light on an emergency vehicle's light bar or as an aircraft warning light. In each case, the projected light has a predetermined intensity distribution, e.g., a uniform intensity profile over the hemisphere.
One type of apparatus of this kind is a translusive diffuser, which includes a sheet of translusive material disposed over a light source. Light from the light source passes through the translusive sheet and is diffused into the surrounding space. Suitable translusive materials include opal glass, acrylics, and Teflon. The translusive sheet sometimes is covered by a transparent protective dome or the sheet, itself, sometimes is formed into a dome shape. Although generally effective in projecting light substantially uniformly, translusive diffusers are considered to be unduly inefficient, projecting only about 20% to 25% of the available light when configured as a hemispherical light distributor.
Another type of apparatus of this kind is a beam redirector, which includes an optical device having a special refractive or reflective surface for redirecting light from a light source such as a laser into a hemisphere. Although such beam redirectors are relatively inexpensive to manufacture, they typically require a critical alignment between the light source and the optical device, and they typically require the use of a light source that provides a light beam having a known, stable intensity distribution. Moreover, the projected light often has a spatial intensity distribution that varies excessively.
It should, therefore, be appreciated that there is a need for an apparatus that projects electromagnetic radiation over a predetermined spherical sector, e.g., a hemisphere, with a tailored spatial intensity distribution, wherein the radiation is projected with greater efficiency and with less dependence on a critical alignment of optical components. The present invention fulfills this need.